I am doing some testing of Maya Sprite rendered with Arnold.
Here is a test scene:
At the moment the setup is not working. I get the same sprite image (number 1) on all the sprites, and the sprites are all oriented the same. I think the problem is that the spriteTwistPP and spriteNumPP attributes are not being passed to the renderer.
After contacting Solid Angle support, it seems that this workflow is not currently supported, but their developers are 'looking at it', which probably means that they will fix it quite quickly.
I will update this post when I have more information.